Flow control of process gas in semiconductor manufacturing

ABSTRACT

A flow control system and method for controlling batchwise delivery of process gas for semiconductor manufacturing are disclosed, wherein the flow control system is operable in a flow mode for delivery of a batch of process gas in a delivery period of time and, alternately, in a no-flow mode. After the start of the delivering, the pressure drop of the gas in a reference capacity of the system is measured for a measurement period of time while interrupting the flow of process gas from a source of the process gas to the reference capacity and continuing to deliver process gas from the system to a semiconductor manufacturing apparatus at a controlled flow rate. The rate of pressure drop in the reference capacity during the measurement period of time is used as a measure of the actual flow rate. Where the actual flow rate does not agree with a specified flow rate for delivering, the controlled flow rate for a subsequent delivery period of time in which another batch of process gas is delivered, is adjusted. Components of the flow control system are arranged along a gas manifold in the form of an elongated delivery stick having a width of less than 1.5 inches, saving important space in a group of the flow control systems that may comprise up to 20 units.

RELATED APPLICATION

[0001] Reference is made to commonly owned Provisional Application Ser.No. 60/133,295, filed May 10, 1999, for “Fluid Pressure Regulator withDifferential Pressure Setting Control”, the disclosure of which isincorporated by reference.

TECHNICAL FIELD

[0002] The present invention relates to a flow control system and methodfor controlling the batchwise delivery of process gas to a semiconductormanufacturing tool. Functional components of the system are assembled ona gas manifold in the form of a narrow delivery “stick”.

BACKGROUND

[0003] The semiconductor manufacturing process includes a phase in whichthe process gas is delivered to the tool according to a program thatspecifies a flow for a period of time. The flow rate is established by amass flow controller, which is supplied with process gas at a regulatedpressure. The output of the mass flow controller is delivered to themanufacturing tool through a pneumatically operated on/off shut-offvalve. The delivery is started by actuating the shut-off valve to openand energizing the mass flow controller to deliver a flow at a presetvalue. The delivery is stopped by actuating the shut-off valve to closeand de-energizing the set point of the mass flow controller.

[0004] An important consideration is the accuracy with which the flow isdelivered during the process phase. To that effect, it is recommended toset the mass flow controller at a value between 40 and 100% of its fullscale. In other words, a given mass flow controller has a rangeabilityof 2.5 to 1. Also, the mass flow controller must be calibrated for thespecific gas to which it is applied. This means that in order to cover arange of flows from 5 to 1000 standard cubic centimeters per minute(sccm), as many as six mass flow controllers for any given gas may berequired. The accuracy consideration also requires that the mass flowcontroller retain its calibration for some period of time, preferably aslong as possible.

[0005] A dynamic gas flow controller is disclosed in U.S. Pat. No.5,865,205 to Wilmer, for controlling the delivery of a gas from areservoir to a semiconductor process chamber. The method and apparatusdisclosed therein involve determining an initial mass of the gasresiding within the reservoir prior to a delivery operation and thefinal mass of gas residing in the reservoir when the flow of gas to theprocess chamber is terminated. The initial mass and final mass of gasvalues are compared to determine the actual mass of gas released fromthe reservoir during the recipe step. This value serves as an input to acalibration servo loop to update the system calibration constant for asubsequent gas delivery recipe step. The execution of the calibrationservo loop serves as a continuous self calibration of a dynamic servoloop, wherein the flow of gas to the process chamber is metered by avariable flow valve upstream of an orifice. The gas pressure createdahead of the orifice during delivery is sensed to measure the gas flowrate.

[0006] In the patent to Wilmer, the concept of flow control applies to agas flowing out of a reservoir instead of a gas flowing in a line. Thecontrol signal which operates the variable flow valve is determined by acircuit in which an input signal (representing the desired flow) isintegrated over the duration of the delivery step to define the desiredvolume/mass. The desired volume is compared to the actual volume takenout of the reservoir. A control signal is generated as a function ofthat comparison and applied as a set point to the control circuit. Inthe dynamic control circuit, the set point is compared to the pressuresignal sensing the flow and a control signal is applied to the variableflow valve to create the desired pressure/flow. That is, in Wilmer, theflow signal is integrated over time and compared to the actual volume.The control signal is applied to the flow control, which consists of thevariable flow valve creating a pressure ahead of the orifice.

[0007] The patent to Kennedy, U.S. Pat. No. 4,285,245, discloses amethod and apparatus for measuring and controlling volumetric flow rateof gases in a line. The patent is of interest for its disclosure of amethod of determining the flow rate of gas flowing in a line by imposinga uniform flow rate at a point downstream of a flow measurement chamberin the line, restricting temporarily the flow at a point upstream of thechamber and measuring the pressure decrease in the chamber between theupstream and the downstream points during part of the duration of therestricted flow, the rate of the pressure decrease being substantiallyproportional to the volumetric flow rate. The patent to Kennedy does notrelate to the batchwise delivery of process gas for semiconductormanufacturing or a flow control system therefor operable in a flow modefor the accurate delivery of a batch of process gas and, alternately, ina no-flow mode.

[0008] There is a need for an improved method and flow control systemfor controlling the batchwise delivery of process gas for semiconductormanufacturing, which can complement a conventional delivery stick by theaddition of only a few components, and which will allow verification ofthe accuracy of the flow delivered in an active phase. There is also aneed for an improved method and flow control system for controlling thebatchwise delivery of process gas for semiconductor manufacturing whichincrease the effective range of the mass flow controller, ensurelong-term stability of the calibration and eliminate the need topre-calibrate for specific gases.

SUMMARY

[0009] The method of the invention for controlling the batchwisedelivery of process gas for semiconductor manufacturing using a flowcontrol system of the invention operable in a flow mode for delivery ofa batch of process gas and, alternately, in a no-flow mode, comprisesdelivering a batch of process gas from a source of pressurized processgas through a flow line of the flow control system to a semiconductormanufacturing apparatus at a controlled flow rate for a delivery periodof time. The line of the flow control system includes a pressureregulator for establishing a regulated pressure of the process gas inthe line, an on/off valve downstream of the pressure regulator to startand stop the flow mode during which the process gas is delivered to theapparatus for the delivery period of time and, upstream in the line fromthe pressure regulator, a reference capacity used to measure the actualflow rate of the delivery.

[0010] The method further comprises, after the start of the deliveringof the batch of process gas, measuring for a measurement period of timethe pressure drop of the process gas in the reference capacity whileinterrupting the flow of process gas through the line to the referencedcapacity and continuing to deliver process gas from the line of the flowcontrol system to the semiconductor manufacturing apparatus at thecontrolled flow rate. The rate of pressure drop in the referencecapacity during the measurement period and the actual flow rate of thebatch of process gas being delivered are determined from the measuring.In case the actual flow rate does not agree with a specified flow ratefor the delivering, the controlled flow rate is adjusted in thedirection of the specified flow rate from the actual flow rate for asubsequent delivery period of time in which another batch of process gasis delivered.

[0011] A flow control system according to the invention is for usewithin a fluid circuit having a source of pressurized gas to bedelivered batchwise at a controlled flow rate to a destination by theflow control system. The flow control system is operable in a flow modefor delivering a batch of gas and, alternately, in a no-flow mode. Theflow control system comprises a flow line through which gas from thesource of pressurized gas can be delivered, a pressure regulator in theflow line to establish a regulated gas pressure in the line, an on/offvalve in the line downstream of the pressure regulator to start and stopthe flow mode during which the gas is delivered for a delivery period oftime, a reference capacity in the flow line upstream of the pressureregulator for use in measuring the actual flow rate of gas beingdelivered by the flow control system, a pressure sensor to measure apressure drop of the gas in the reference capacity during a measurementperiod of time commencing after the start of a delivery period of time,means in the line upstream of the reference capacity for interruptingthe flow of the gas from the source of pressurized gas to the referencecapacity during delivery of the gas by the flow control system, and acontroller for determining from the measured pressure drop the rate ofpressure drop in the reference capacity during the measurement periodthe actual flow rate of a batch of process gas being delivered and, incase the actual flow rate does not agree with a specified flow rate forthe delivering, adjusting the controlled flow rate in the direction ofthe specified flow rate from the actual flow rate for a subsequentdelivery period of time in which another batch of process gas isdelivered.

[0012] In one embodiment of the invention, the flow control arrangementof the system comprises a mass flow control valve in the line downstreamof the pressure regulator. The controller of the system adjusts a setpoint value of the mass flow control valve for adjusting the controlledflow rate. Advantageously, the mass flow control valve has a range ofpossible controlled flow rate settings which extends to 100% of its fullscale with an effective rangeability of 10:1.

[0013] According to another form of the invention, the flow controlarrangement of the system comprises a fixed orifice in the flow linedownstream of the pressure regulator. The pressure regulator has anadjustable pressure setting for adjusting the controlled flow rate.

[0014] The flow control system of the invention uses functionalcomponents compatible with a 1 ⅛ inch width manifold. The assemblyfeatures surface mounting on a modular base. A significant benefit is toreduce the length of the delivery stick and to make it possible to placethe parallel manifolds side-by-side at a distance of 1.2 inches betweencenter lines instead of the current 1.6 inches. In the flow controlsystem employing a mass flow control valve, increasing the effectiverangeability of the controller from 2.5 to 1 up to 10 to 1, makes itpossible to cover flows from 5 to 1000 sccm with only three ranges:1000, 200 and 50 sccm. The long term stability of calibration is alsoensured through automatic calibration during each active phase and theneed to calibrate for each specific gas is eliminated.

[0015] These and other features and advantages of the present inventionwill become more apparent from the following detailed description ofseveral embodiments of the present invention taken with the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

[0016]FIG. 1A is a schematic illustration of a flow control system forbatchwise delivery of process gas in semiconductor manufacturingaccording to one embodiment of the invention.

[0017]FIG. 1B is an enlarged schematic drawing of a portion of the flowcontrol system of FIG. 1A along a narrow elongated manifold or delivery“stick” of the system having components of the system mounted thereon.

[0018]FIG. 2A is a schematic illustration of a flow control system forbatchwise delivery of a process gas in semiconductor manufacturingaccording to a second embodiment of the invention.

[0019]FIG. 2B is an enlarged, schematic drawing of a portion of the flowcontrol system of FIG. 1B along a narrow, elongated manifold or deliverystick supporting components of the system.

[0020]FIG. 3 illustrates a flow chart of one embodiment of theinvention.

[0021]FIG. 4 is a cross-sectional view of a diaphragm-type pressureregulator which can be used in the flow control system of the invention,the regulator including a manually adjustable main pressure settingassembly, and a pneumatically controllable differential pressure settingassembly which is actuable to apply a differential force on theregulator diaphragm independent of the main pressure setting force.

[0022]FIG. 5 is a magnified view of the regulator of FIG. 4 showing themanual main pressure setting adjustment thereof in enforced detailed.

[0023]FIG. 6 is a representative pressure response of a the regulator ofFIGS. 4 and 5 with a controlled differential pressure setting, theresponse being shown as the regulator outlet pressure traced as a cyclicfunction of time and as compared to the response of a regulator which isconventionally operated at a constant pressure.

[0024]FIGS. 7A and 7B are front and back views, respectively, of thecontroller of the flow control systems of FIGS. 1A and 1B and FIGS. 2Aand 2B.

[0025]FIG. 8 is an electrical-pneumatic diagram of the flow controlsystem of FIGS. 1A and 1B.

[0026]FIG. 9 is an electrical-pneumatic diagram of the flow controlsystem of FIGS. 2A and 2B.

DETAILED DESCRIPTION

[0027] The semiconductor industry utilizes the batchwise delivery ofprocess gases in the manufacture of integrated circuit (IC) chips ordies. In the general mass production of semiconductor devices, hundredsof identical “integrated” circuit (IC) trace patterns arephotolithographically imaged over several layers on a singlesemiconductor wafer which, in turn, is cut into hundreds of identicaldies or chips. Within each of the die layers, the circuit traces aredeposited from a metallizing process gas such as tungsten hexafluoride(WF₆), and are isolated from the next layer by an insulating materialdeposited from another process gas. The process gases typically aredelivered in discrete flow cycles or “batches” from pressurizedsupplies, thereby requiring delivery systems of a type which may beoperated in alternate flow and no-flow modes.

[0028] An improved flow control system 10 according to the invention forthis purpose is shown in the schematic of FIG. 1. Referring to FIG. 1,the system 10 may be seen to comprise a flow line 1 through which gasfrom a pressurized process gas supply 12 can be delivered batchwise to asemiconductor manufacturing tool 2. The system 10 is operable in a flowmode for delivering a batch of gas and, alternately, in a no-flow mode,by means of controller 3, for example, a suitably programmed computer.

[0029] The flow control system 10 further comprises a pressure regulator16 in the flow line 1 to establish a regulated gas pressure in the line.An on/off valve 24 in the line 1 downstream of the pressure regulator 16is actuated by the controller 3 to start and stop the flow mode duringwhich the gas is delivered for a delivery period of time. The valve 24is a pneumatically operated valve in the disclosed embodiment, see theschematic pneumatic-electrical diagram of FIG. 8.

[0030] A reference capacity 5 is provided in the flow line 1 upstream ofthe pressure regulator 16 for use in measuring the actual flow rate ofgas being delivered by the flow control system as discussed below. Apressure sensor 6 in the form of a pressure transducer is located in theline 1 adjacent the reference capacity 5 to measure a pressure drop ofthe gas in the reference capacity during a measurement period of timecommencing after the start of a delivery period of time.

[0031] The reference capacity 5 incorporates a temperature sensingelement to measure the temperature of the gas inside the capacity. Thetemperature value is used by the controller, in conjunction with therate of pressure decrease, to determine the actual flow expressed forstandard conditions [14.7 psia and 20° C. (293° K. )]. The flow forstandard conditions is:${{{Qsccm}@20^{{^\circ}}}{C.}} = {\frac{V}{14.7} \times \frac{\Delta \quad P}{\Delta \quad t} \times \frac{293}{T}}$

[0032] V is the volume of the capacity in cc$\frac{\Delta \quad P}{\Delta \quad t}$

[0033]  is the rate of pressure change in psi/min

[0034] T is the temperature in °K.

[0035] A means 14, a pneumatically operated valve in the illustratedembodiment, in the line 1 upstream of the reference capacity 5 can beset in an off position by the controller 3 for interrupting the flow ofprocess gas from the source 12 to the reference capacity 5 duringdelivery of the gas to the tool 2 by the flow control system.

[0036] According to the method of controlling the batchwise delivery ofprocess gas for semiconductor manufacturing using the flow controlsystem 10 of the invention, a batch of process gas is delivered from asource of pressurized process gas through the flow line 1 of the flowcontrol system 10 to the semiconductor manufacturing apparatus 2 at acontrolled flow rate for a delivery period of time. After the start ofthe delivering of the batch of process gas, the pressure drop of theprocess gas in the reference capacity is measured for a measurementperiod of time while interrupting the flow of process gas through theline to the reference capacity with the valve 14 and continuing todeliver process gas from the line of the flow control system to thesemiconductor manufacturing apparatus 2 at the controlled flow rate.

[0037] From the measured pressure drop of the process gas in thereference capacity for the measurement period of time, the rate ofpressure drop in the reference capacity and, in turn, the actual flowrate of the batch of process gas being delivered, are determined. Incase the actual flow rate does not agree with a specified, desired flowrate for the delivering, the controlled flow rate of delivery by thesystem is adjusted in the direction of the specified flow rate from theactual flow rate for a subsequent delivery period of time in whichanother batch of process gas is delivered. In the disclosed embodimentof FIGS. 1A and 1B, this determining and adjusting is performed bycontroller 3, a programmed computer. The controller 3 adjusts a setpoint value of the mass flow control valve 22 by a signal sent by thecontroller for adjusting the controlled flow rate for a subsequentdelivery period of time in which another batch of process gas isdelivered. For this purpose, the controller 3 includes a referencememory 28 storing a mathematical relationship between the actual flowrate and the flow rate setting of the mass flow control valve forreference in determining the size of the adjusting of the controlledflow rate so that the difference between the two values is reduced tozero in the subsequent delivery period of time.

[0038] The flow control system 10 further comprises a gas manifold 7 inthe form of an elongated delivery stick having a width less than 1.5inches. Components of the flow control system are arranged along the gasmanifold in communication with the flow line 1 which extends through themanifold and to each of the components mounted on the upper surface ofthe manifold. Thus, the gas manifold 7 serves as a mounting base forthese components. The mounting base has a width of 1.125 inches in thedisclosed embodiment. This allows placing a plurality of the flowcontrol systems side-by-side at a distance of 1.20 inches between theparallel center lines, thus saving important space in a group that maycomprise up to 20 units. The pneumatically operated valve 8 can beselectively opened to allow a purge gas to be passed through the flowline of the flow control system.

[0039] The flow control system to be used in conjunction with aconventional mass flow control valve 22, offers a significantimprovement by increasing the effective rangeability of the mass flowcontrol valve from 2.5 to 1 up to 10 to 1, making it possible to coverflows from 5 to 1000 sccm with only three ranges: 1000, 200 and 50 sccm.The flow control system also eliminates the need to calibrate the systemfor each specific gas and ensures the long term stability of thecalibration through automatic recalibration during each delivery phasefor the next phase.

[0040] The method of controlling the batchwise delivery of process gasfor semiconductor manufacturing using the flow control system involvessetting the desired flow value as a percent of full scale by setting thedesired flow setting of the flow controller 3 for making delivery ofprocess gas. The actual flow during the delivery phase is measured andthe command to the mass flow control valve is adjusted so that theactual flow is kept equal to the set point value in the followingdelivery phase(s). This operation may be repeated at each delivery phaseor after a desired number of delivery phases. The actual flow ratedetermined by measuring the pressure change in the reference capacity 5is expressed in standard units and applies essentially to any gas. Theactual value is compared to the desired set point value. If there is anydifference between the two values, the flow control system modifies thecommand signal sent to the mass flow control valve 22 so that thedifference (error signal) is reduced to zero.

[0041] A digital display 40 in FIGS. 7A and 8, on the controller allowsthe operator to read, alternately, by switching switch 41, the set pointflow value and the actual flow value. The set point value may beadjusted by actuating up and down pushbuttons 42 and 43. A second switch44 allows to start and stop delivery of the process gas. Typically, thepressure regulator 16 is set to supply the mass flow control valve 22 ata regulated pressure of 10-15 psi. The small reference capacity 5 usedto measure the actual flow is mounted directly upstream of the pressureregulator. The pressure transducer 6 measures the pressure in thecapacity. The pneumatically operated on/off valve 14 is mounted upstreamof the capacity. When the valve 14 is open, it supplies the capacitywith process gas from the supply line at a typical pressure of 40-50psi. It is not required to regulate precisely the supply pressure to thesystem 10. It can be anywhere between 45 and 60 psi, for example.

[0042] Prior to the start of a delivery phase, the supply on/off valve14 is opened and the reference capacity 5 is filled at the supplypressure. The pressure regulator 16 maintains a constant pressure at theinlet of the mass flow control valve 22. At the start of a givendelivery operation, which lasts typically from 20-40 seconds, the on/offvalve 24 downstream of the mass flow control valve 22 is actuated toopen and the mass flow control valve is energized to deliver flow at theset point value. The measurement period begins after the start of thedelivery, e.g., 1 second after the start of the delivery. With continueddelivery of the process gas, the pressure in the reference capacity 5decreases progressively. The measurement period continues for a maximumduration of 20 seconds or is terminated when the pressure in themeasurement capacity reaches a predetermined value such as 20 psi. Atthe end of the measurement period, the flow indication displayed atdisplay 40 on the controller 3 is updated to agree with the measuredexact value and, if necessary, any correction factor is determined to beapplied to the next delivery phase. The change in pressure at the inletof the pressure regulator, which occurs at the end of the measurementperiod, does not affect the regulated outlet pressure, which istypically set at 10-15 psi as noted above. Thus, the pressure in thereference capacity 5 is allowed to go from a nominal value of 50 psidown to a limited value of 20 psi. The measurement period will belimited to the maximum of 20 seconds at lower flow values. At higherflow values, the 20 psi limit may occur before the 20 second limit.

[0043] At the beginning of the delivery phase, the flow indicator 40 onthe controller will display the flow value of the previous delivery.Then it will change to an indication of the current flow when themeasurement period is completed. As the measurement period isterminated, the on/off valve 14 at the supply side is actuated to openand the pressure in the reference capacity 5 returns to the supplylevel. This does not affect the regulated pressure applied to the inletof the mass flow control valve.

[0044] The flow control system 10′ in the embodiment of FIGS. 2A and 2Beliminates the need of the mass flow control valve 22 and its attendantshut-off valve. The flow control is provided by a pressure regulator 16′and an orifice 36 incorporated in the seat of on/off valve 20. For agiven orifice, the flow is proportional to the absolute pressure appliedto it by the pressure regulator 16′. In this application, the set pointof the pressure regulator is established by a pressure signal applied tothe dome of the pressure regulator. The pressure signal is created by anelectric/pneumatic convertor 38, see FIGS. 2A and 9, which generates apressure proportional to the input voltage from the controller(analogous to the signal applied to the mass flow control valve). Anydifference (error signal) between the set point and the measured flow isused to correct the pressure signal applied to the dome of the pressureregulator as in the operation of the flow control system of FIGS. 1A and1B. At the end of the delivery phase, the on/off valve 20 downstream ofthe orifice 36 is actuated to close and the pressure signal is removedfrom the dome of the pressure regulator 16′. This keeps the pressureupstream of the orifice 36 at the set point value and prevents the creepthat would normally occur at the outlet of the pressure regulator in ano-flow condition. The given orifice may be used to deliver flow with arangeability of 10:1, making it possible to cover flows from 5-1000 sccmwith only three orifice sizes corresponding to 1000, 200 and 50 sccm.

[0045] The operating sequence of a program for a flow control systemaccording to the invention, particularly the flow control system ofFIGS. 1A and 1B, is shown in the flow chart of FIG. 3. With reference toa functional demonstration of the control system, it is noted that themass flow control valve 22 of the system in the disclosed embodiment hasa range of 200 sccm. The pressure regulator is set at a nominal 10 psi(25 psia). The nominal volume of the reference capacity is 20 cc. Thepressure transducer 6 has a range of 0-100 psia. The supply to thereference capacity 5 is at a nominal value of 50 psi (65 psia). It doesnot have to be very precise (±2 psi) as indicated above.

[0046] A first operation as referred to in FIG. 3 is to establish thecalibration factor for the flow control system at mass flow controlvalve setting of 100%. To accomplish this, the flow check switch 45 onthe controller is set to “yes” and a delivery run of process gas is madewith the setting of the controller 3 at 100% and the actual flow beingdelivered is read with a calibrated flow meter. This establishes therelationship between the flow indicated by the digital display 40 (in %)on the controller 3 and the actual flow. The calibration factor is thencreated in the controller which makes 100% indication correspond to thedesired full scale of 200 sccm. Example: the calibration run delivers220 sccm and the flow indication is 120%. The calibration factor toobtain 100% and 200 sccm will be 100/120×200/220=0.75. With thecontroller switch 44 at “stop” and the display switch 41 at “setting” soas to display the calibration factor on digital display 40, the newfactor is set by using the up and down buttons 42 and 43 on thecontroller 3. Another delivery run is then made to verify that the flowis 200 sccm and the indication is 100%. The procedure can be repeated ifnecessary.

[0047] The next step in the process is to establish a mathematicalrelationship between the actual flow and flow setting over the range ofthe mass flow control valve flow settings. This is obtained by making adelivery run at 100% setting, followed by a delivery run at 10% settingand determining the actual flow (measured by the controller) in eachrun. That transfer function is established within the controller whereit is used to calculate the control signal to be sent to mass flowcontrol valve so that the flow remains equal to the setting. Thefollowing sequence creates the calibration runs: set the display switch41 to “setting” and the flow operation switch 44 to “stop”; push the twobuttons 42 and 43 and hold until the calibration factor is displayed;and then set display switch 41 to “flow”. This initiates the twosuccessive delivery runs.

[0048] The next step is to set a desired flow setting of the flowcontroller 22 for making a delivery of process gas, for example, 80%.This is done by adjusting with the up and down push buttons 42 and 43 onthe controller 3 while the display switch 41 is set to “setting”. Theflow check switch 45 on the controller is set to “yes”. Delivery isstarted by switching flow switch 44 to “start”. The display switch 41 isset to “flow” and the indication of flow is watched on digital display40 during the delivery. At the end of the measurement period, the flowindication on the display will be updated. The start of the updatedvalue will be flashed briefly (1-2 seconds). The delivery is stopped byswitching flow switch 44 to “stop”. In the case the flow check switch 45on the controller 3 were set to “no”, the flow indication on the display40 would remain unchanged for the length of the delivery. This mode ofoperation may be selected if it is felt that the flow controller 3 needscalibration verification only periodically.

[0049] The setting is then changed to 50%, the flow check is set to“yes” and another delivery is started and the flow indication on thedisplay is watched. Initially, the flow indication will be close to 50%.At the end of the measurement period, the actual flow value will beshown. If it is not 50%, a correction will be calculated, to be appliedto the next delivery. It may take two or three runs to establish theflow value at 50±0.1%. The setting can then be changed to 20% and theprocedure repeated. Likewise, the setting is changed to 10% and theprocedure repeated.

[0050] A functional demonstration of the flow control 10′ of theembodiment of FIGS. 2A and 2B involved the use of an on/off valve 20which incorporated an orifice 36 having a diameter of 0.004 inch in itsseat. This provides a flow of 10 to 150 sccm as the regulated pressureis controlled from 2.5 to 25 psia. To establish a calibration factor,the aforementioned procedure is used to obtain an operating condition of150 sccm at 100% indication. Next a calibration run is made to establishthe transfer function or mathematical relationship. Practice deliveryruns can then be made at 80, 50, 20 and 10% as in the previousfunctional demonstration.

[0051] In both functional demonstrations, the flow control system 10 ¹is used to provide a flow setting, read the actual value of the flowdelivered, start and stop a delivery phase and select flow verificationat each delivery or periodically, as desired. In the ultimateconfiguration, the functions displayed and incorporated within the flowcontrol system are implemented in the central computer of the machine aswill be understood by the skilled artisan from a reading of applicant'sdisclosure.

[0052] According to a further feature of the present invention, theconventional pressure regulators 16 and 16′ of the embodiments of FIGS.1A, 1B and 2A, 2B can be replaced with the pressure regulator 50 shownin FIGS. 4 and 5 for mitigating the effect of pressure creep and, whenthe flow control systems are operated in the alternate flow and no-flowmodes, allowing faster pressure response and steady-state operation forimproved process gas utilization or other system economy. This pressureregulator is disclosed in commonly owned Provisional Application Ser.No. 60/133,295, filed May 10, 1999.

[0053] In basic construction, the regulator 50 includes a housing,referenced at 52, which may comprise a generally annular, upper capportion, 54, and a lower body portion, 56. An associated nut, 58, may bereceived over a flanged lower end, 60, of the cap 54 for a threadedconnection with an externally-threaded upper end, 62, of body 56. Capand body portions 54 and 56 thereby may be engaged to define an internalchamber, 63, within housing 52. Upper and lower support plates, 64 and65, respectively, are clamped between the cap and body portions 54 and56 for supporting other regulator components. Each of plates 64 and 65are formed as having a central opening, 66 and 67, respectively. Plate65 further is formed as having a plurality of axially-extending throughbores or channels, one of which is referenced at 68, and is made tocompressively engage a raised annular surface, 69, of body 56 to effecta back-up seal against leakage of the gas or other fluid flowing throughthe regulator 50.

[0054] Body portion 56 of housing 52 itself is formed as having aninternal fluid passageway, 70, which may be divided into generallyL-shaped upstream and downstream portions 71 a and 71 b, each extendingfrom an axial surface, 72, of body 56, to an upper radial surface, 73,thereof. Fluid passageway 70 itself extends between an inlet, 74, and anoutlet, 75, of the regulator for the flow of fluid therethrough in thedirection referenced by arrows 76. Within the fluid circuit in thecontrol systems 10 and 10′ of FIGS. 1A, 1B and 2A, 2B, a high pressureflow of gas is supplied to regulator inlet 74 from supply 127 and aregulated, lower pressure flow is delivered to mass flow control valve22 from regulator outlet 75. In this regard, regulator inlet 74 may becoupled in fluid communication with supply via valve 14, with outlet 75being coupled in fluid communication with mass flow control valve 22 viavalve 20. Each of inlet 74 and outlet 75 accordingly may be configured,as is shown, as flanged tubing extensions, 76 a-b, respectively, whichmay be joined to body portion 56. For connection within the fluid system10, extension 76 a is shown as having an associated female fittingconnector, 78, with extension 76 b being shown as having an associatedmale connector, 80.

[0055] For controlling the flow of fluid through passageway 70, chamber63 houses a valving assembly including a poppet, 82, and an associatedvalve seat, 84, defined within passageway 70 such as by a disc which issupported over the upstream portion 71 a of passageway 70 and clampedbetween the central opening 67 of lower support plate 56 and the openingof passageway portion 71 a into the upper radial surface 73 body portion56. Valve seat 84, is oriented relative to the flow direction 76 ashaving an upstream side, 86, and a downstream side, 88, and includes anaperture, 90, for admitting fluid pressure into a lower plenum, 92, ofchamber 63, which plenum is defined partially by lower support plate 65.Flow out of plenum 92 and into the downstream portion 71 b of passageway70 is accommodated via plate channels 68. The disc for valve seat disc84 preferably is formed of a plastic or other polymeric material, andmost preferably of a fluoropolymer such as Kel-F® (3M, St. Paul, Minn.).

[0056] Poppet 82 is movable along a central longitudinal axis, 94, ofthe regulator 50 between a first position (shown in FIG. 4) closingpassageway 70 to fluid flow for the operation of fluid system (FIG. 1A)in its no-flow mode, and a variable second position throttling the fluidflow through passageway 70 for the operation of system in its flow mode.For cooperation with valve seat 84, poppet 82 is provided to extendalong axis 94 from a lower head portion, 96, disposed opposite theupstream side 86 of valve seat 84, to an upper, elongate stem portion,98, which, in turn, extends through aperture 90 and lower plate opening67 along axis 94 from a lower proximal end, 100, connected to headportion 96, to an upper distal end, 102. Poppet head portion 96 isconfigured, such as the general conic shape shown, to annularly vary therelative size of aperture 90 and, accordingly, the flow rate through theregulator, when moved toward or away from valve seat 84 in the variablesecond poppet position.

[0057] For controlling the movement of poppet 82 along axis 94, adiaphragm, 110, is received within chamber 63 as disposed in fluidcommunication with passageway 70 to define a flexible upper wall ofplenum 92, and as coupled in force transmitting contact with poppet 82.Diaphragm 110 is of a conventional single or multiple piececonstruction, and includes a circumferentially extending, generallyflexible “membrane” portion 112. Membrane portion 112 extends radiallyoutwardly to an outer margin which defines the outer periphery of thediaphragm 110, and which is clamped between the upper and lower plates64 and 65 for the mounting of diaphragm 110 within chamber 63. In atwo-piece construction of diaphragm 110, membrane portion 110 is welded,bonded or otherwise attached to a backup portion, 114, which supportsthe membrane portion 112, and which extends axially therefrom throughthe opening 66 of plate 64 in defining a cylindrical extension, 115,including an internal central passage, 116, and an external shoulder,118. Passage 116 is configured to receive the distal end 102 of poppetstem 98, and may be internally threaded for engagement with anexternally threaded portion, 120, of stem 98. So received in chamber 63,diaphragm 110 is provided to be responsive to a fluid pressure force,which is proportional to the inlet pressure (P_(i)) and outlet fluidpressure (P_(o)) of the fluid flow to regulator 50 and is applied to thedirection referenced at 122 to urge poppet 82 toward its first positionclosing passageway 70 to fluid flow. Atmospheric pressure (P_(a)) isadmitted in chamber 63 on the upper side of diaphragm 110 via port 124through cap 54.

[0058] A main pressure setting assembly, reference generally at 127, isactuable to applying a balancing force on diaphragm 110 in the directionreferenced at 128 for opposing the fluid pressure force 122 and urgingpoppet 82 toward its second position opening passageway 70 to fluidflow. Such force 128 is developed at least in part by the adjustablecompression of a main coil spring, shown in phantom at 130, or otherresilient member received within chamber 63. In the illustratedembodiment of FIG. 4, spring 130 is disposed coaxially with axis 94 forcompression intermediate diaphragm 110 and a manually-adjustable knob,132, which is translatable along axis 94. For a compact design ofregulator 50, knob 132 is externally-threaded as at 134, and is housedwithin cap 54 as threadably rotatably engaged with an internallythreaded portion, 136, thereof. As may be seen best with momentaryreference to the magnified frontal view of main pressure settingassembly 127 shown in FIG. 5, cap 54 is provided as having a window, 140(also shown in phantom in FIG. 4), through which a knurled portion, 142,of knob 132 is provided to be hand accessible.

[0059] Returning to the cross-sectional view of FIG. 4, spring 130 maybe seen to be received within chamber 63 as disposed intermediate anupper retainer, 150, and a lower retainer, 152. Upper spring retainer150 is generally disc-shaped, and is disposed in abutting,force-transmitting contact with a thrust portion, 154, of knob 132.Lower spring retainer 152 is generally cylindrically-shaped, and isreceived coaxially over diaphragm back-up extension 115 as threadablyengaged in force transmitting contact with an externally threadedportion 156, thereof. Retainer 152 is fastened onto extension 115 with anut, 160, which may have an associated O-ring 162, over which the lowerend of spring 130 may be friction fit for assisting the coaxialalignment of the spring with axis 94. A compression ring, 164, or otherspacer may be received with retainer 152 over extension 115 fordelimiting the travel of the retainer over the extension.

[0060] For applying an additional force on diaphragm 110 in thedirection of arrow 122, a wave spring or other compressible member,shown in phantom at 170, is received coaxially over retainer 152. Spring170 is supported on upper support plate 64 for compression therebetweenand a radially-outwardly extending flange portion, 172, of retainer 152.Such compression of spring 170 provides a biasing force for furtherurging poppet 82 toward its first position such that fluid passageway 70is normally closed in the absence of a pressure setting force 128. Themovement of poppet 82 between its first and second positions may bedamped with a compressible foam washer, 174, which is received coaxiallyover diaphragm extension 115 for compression intermediate retainer 152and plate 64. The displacement of poppet 82 in its second position bythe application of pressure setting force 128 is delimited by theabutting engagement of a lower stop surface, 176, of retainer 152 withplate 64.

[0061] Regulator 50 further includes a differential pressure settingassembly, referenced generally at 180. In accordance with the preceptsof the present invention, differential pressure setting assembly 180 isprovided to be actuable independently of the main pressure settingassembly 127 to apply a differential force, such as via the compressionof a second coil spring member, 181, on diaphragm 110 in the directionof arrow 128 further urging poppet 82 toward the second position openingpassageway 70 to fluid flow. In the illustrated embodiment of FIG. 4,differential pressure setting assembly 180 is actuable responsive to apneumatic on/off control signal of a given input pressure (P_(s)) which,preferably, may be between about 50-60 psig to be at the same levelwhich is conventionally employed in operating the pneumatic valves 14and 24 of fluid system of FIG. 1. The signal to assembly 180, as well asvalves 14 and 24 of system 10, may be provided under the common controlof, for example, of a pneumatic 3-way valve (not shown).

[0062] The pressure control signal may be admitted to regulator 50 via atubing or other fitting connection, 182, having, for example, a femaleend, 184, configured for a tubing or other connection to the abovementioned 3-way valve or other control signal source, and male end, 186,configured for a threaded connection with an adapter, 190, of regulatorhousing 52. Adapter 190, in turn, has a male end, 192, configured for athreaded connection with an internally threaded upper end, 194, of cap54, and a female end, 196, which, depending upon the sizing of fittingend 186, may be coupled thereto via a bushing or other reducer, 198. Thefemale end 196 of adapter 190 further is configured as having a recesswhich extends to internal end wall, 200, that defines a second chamber,202, within housing 52. The adapter male end 192 further is configuredas having an elongate guide portion, 204, which is fitted within agenerally cylindrical counter bore, 206, of knob 132 to assist inguiding the knob along axis 94.

[0063] For controlling the compression of second spring member 181, apiston, 210, having an associated O-ring or other seal or packing ring,211,is received within chamber 202 as displaceable intermediate lowerend wall 200 and an upper end wall, 212, of chamber 202. Upper end wall212 is defined, such as by a radially-inwardly extending internalshoulder portion of reducer 198, about a common opening, 214, of adapter190 and reducer 198, which opening 214 functions as a port for theadmission of the signal fluid pressure into chamber 202.

[0064] Piston 210 is operably coupled to spring 181 via an elongateforce transmitting member, 220. Such member 220 extends along axis 94,as received coaxially through a central bore, 222, formed through eachof adapter 190, knob 132, and spring retainer 150, from an upper end,224, disposed in abutting contact with piston 220, to a lower end, 226,disposed in abutting contact with spring 181. spring 181 itself isdisposed coaxially within main pressure setting spring 130 as mountedover diaphragm extension 115 for compression between the shoulderportion 118 thereof, and an inverted U-shaped retainer, 228, interposedbetween spring 181 and the lower end 226 of elongate member 220.

[0065] Within chamber 202, piston 210 is actuable responsive to thecontrol pressure signal as admitted through opening 214 and applied toan upper surface, 230, of the piston. That is, piston 210 isdisplaceable along axis 94 from a normally-biased upper position to thelower position shown in FIG. 4. For biasing piston in its upperposition, a compressible spring coil, 232, may be received within arecess, 234, formed within a lower surface, 236, of the piston forcompression against adapter lower end wall 200. In its lower position,piston 210 depresses elongate member 220 which, in turn, effects thecompression of spring 181 to apply a differential force, which may bebetween about 3-4 psig, on a diaphragm 110. In this way, a controlledapplication of the differential force may be achieved independent of theapplication of the main pressure setting force.

[0066] The force applied by spring 181 is “differential” in that it maybe applied as a step function to effect a proportionate change in theregulator outlet pressure without changing the main pressure setting.for example, with the main pressure setting assembly 127 of regulator 50being adjusted within a range of between about 0-30 psi, differentialpressure setting assembly 180 is actuable by the control signal toincrease the effective regulator setting by a nominal 3 psi. If desired,the pressure of the control signal may be adjusted to effect a generallyproportional increase or decrease in the differential force.

[0067] Considering the next operation of regulator 50 of the inventionas employed in the fluid circuit of the batchwise gas delivery circuitof FIG. 1 (with regulator 50 of the invention being substituted thereinfor regulator 16), reference may be had additionally to FIG. 6 wherein atypically response of regulator 50 within such circuit is graphicallyportrayed at 250 as plot of outlet pressure (P_(o)) versus time (t). Fora given inlet fluid pressure, which may be between about 50-60 psi, anda specified outlet pressure set point of about 15 psi, the system isoperated prior to time t_(o) in a flow mode, In such mode, gas isdelivered through regulator 50 at a steady-state flow rate of, forexample, 200 sccm and a regulated outlet pressure of about 14.8 psi.Such pressure is effected under the control of the main pressure settingof the regulator 50 which is adjusted to a nominal pressure of 12 psi,and with signal pressure being supplied to the regulator to apply adifferential pressure which is normally 3 psi. Both the main and thedifferential pressure settings may be set at a lower flow rate of, forexample, 50 sccm. In this regard, it may be noted that the actualregulator outlet pressure at steady flow is about 0.2 psi less than theset point due to the effect of “droop” as the flow rate is increasedfrom low flow to its steady-state value.

[0068] At about time t_(o), corresponding to the termination of the flowmode, the mass flow control valve 22 (FIG. 1) is commanded “off”.Shortly thereafter, i.e., 0.5 sec or less, pneumatic on/off valve 24 isactuated to close such that fluid flow decreases from the steady-staterate to zero. Generally simultaneously with the actuation of valve 24,signal pressure is discontinued to regulator 50 to remove thedifferential pressure setting. In this regard, the operation of valve 24and regulator 50 advantageously may be synchronized under the control ofa common signal pressure.

[0069] With the differential pressure setting being removed, the settingof regulator 50 effective is reduced to 12 psi. Inasmuch as the outletpressure remains at the operating pressure of 14.8 psi, the regulatorcloses such that the outlet pressure is maintained substantially at 14.8psi. Depending upon the length of the no-flow period and/or on theinternal, typically about 0.5 sec, between when the no-flow mode isinitiated and when the control pressure signal is removed to effect theclosing of the regulator, the outlet pressure may increase slightly, toperhaps 15 psi, over the period Δt_(o). It will be appreciated, however,that by virtue of the controlled differential pressure setting, noappreciable creep effect is evident even when the system is operatedwith very long internals, i.e., 1 hour or more, between the flow modes.continuing then along trace 250, at time t₁, corresponding to theinitiation of the next flow mode, the pressure signal is resumed to openvalve 24 and to re-apply the differential force on the regulator.Shortly thereafter, the mass flow control valve 22 is commanded to againcontrol flow. In such operation, flow may be increased from zero to asteady-state value before any appreciable increase in the outletpressure as a result of creep induced from the effective change in theregulator setting from 12 psi to 15 psi. Thus, as the flow rateincrease, the outlet pressure decreases only about 0.2 psi to settlequickly at the operating pressure within a very short period Δt₁ ofabout 0.5 sec. or less. Importantly, as no overshoot or otheroscillatory effects are observed, the transition from zero tosteady-state flow is able to be established within 1 sec or less.

[0070] For purposes of comparison, the pressure trace of a regulatorconventionally operated at a constant pressure setting of 15 psi isshown at 250′. At time t_(o) and continuing over the period Δt_(o)′which may be 100 sec or more, the outlet pressure of trace 250′ may benoticed to increase by about 2 psi from the operating pressure. Ascompared to the 0.2 psi increase for valve 50 of the invention, suchincrease is significant, as is the period Δt₁′ which may be 1.5 sec ormore with some overshoot or other oscillatory effects being evident.

[0071] Thus, in the disclosed flow control system and method, thisunique and efficient fluid pressure regulator construction and method ofoperation mitigate the effect of pressure creep and, when the flowcontrol systems are operated in alternate flow and no-flow modes, allowfaster pressure response and steady-state operation for improved processgas utilization or other system economy.

[0072] Unless otherwise specified, materials of construction are to beconsidered conventional for the uses involved. Such materials generallywill be corrosion resistant and otherwise selected for compatibilitywith the fluid being transferred or for desired mechanical properties.

[0073] As it is anticipated that certain changes may be made in thepresent invention without departing from the precepts herein involved,it is intended that all matter contained in the foregoing descriptionshall be interpreted in an illustrative rather in a limiting sense.

I claim:
 1. A method of controlling the batchwise delivery of processgas for semiconductor manufacturing using a flow control system operablein a flow mode for delivery of a batch of process gas and, alternately,in a no-flow mode, said method comprising: delivering a batch of processgas from a source of pressurized process gas through a flow line of saidflow control system to a semiconductor manufacturing apparatus at acontrolled flow rate for a delivery period of time, said line of theflow control system including a pressure regulator for establishing aregulated pressure of said process gas in said line, an on/off valvedownstream of said pressure regulator to start and stop said flow modeduring which said process gas is delivered to said apparatus for saiddelivery period of time and, upstream in said line from said pressureregulator, a reference capacity used to measure the actual flow rate ofsaid delivering, after the start of said delivering of said batch ofprocess gas, measuring for a measurement period of time the pressuredrop of said process gas in said reference capacity while interruptingthe flow of process gas through said line to said reference capacity andcontinuing to deliver process gas from said line of said flow controlsystem to said semiconductor manufacturing apparatus at said controlledflow rate, determining from said measuring the rate of pressure drop insaid reference capacity during said measurement period and the actualflow rate of said batch of process gas being delivered and, in case saidactual flow rate does not agree with a specified flow rate for saiddelivering, adjusting said controlled flow rate in the direction of saidspecified flow rate from said actual flow rate for a subsequent deliveryperiod of time in which another batch of process gas is delivered. 2.The method according to claim 1, wherein said flow control systemfurther comprises a mass flow control valve downstream of said pressureregulator, and wherein said adjusting of said controlled flow rateincludes adjusting a set point value of said mass flow control valve. 3.The method according to claim 1, wherein said flow control systemfurther comprises a fixed orifice in said flow line downstream of saidpressure regulator, and wherein said adjusting of said controlled flowrate includes adjusting a pressure setting of said pressure regulator.4. The method according to claim 3, wherein said pressure regulator is adome loaded pressure regulator whose pressure setting is established bya fluid pressure applied to the dome of the pressure regulator, and saidmethod including at the end of said delivery period of time removing thepressure signal applied to the dome of the pressure regulator to preventcreep at the outlet of the pressure regulator in a no-flow mode.
 5. Themethod according to claim 1, wherein said flow control system can beadjustably set to establish said controlled flow rate of gas deliverywithin a range of possible controlled flow rates depending upon thesetting of said flow control system, and said method further includingestablishing a mathematical relationship between the actual flow rateand the flow rate setting of said flow control system and in case saiddetermined actual flow rate of said batch of process gas being delivereddoes not agree with said specified flow rate for said delivery,referring to said mathematical relationship in determining the size ofsaid adjusting of said controlled flow rate.
 6. The method according toclaim 5, including storing said mathematical relationship in a referencememory of said control system for said reference thereto.
 7. The methodaccording to claim 5, wherein said flow control system includes a massflow control valve having a range of possible controlled flow ratesettings which extends to 100% of its full scale with an effectiverangeability of 10:1.
 8. The method according to claim 1, wherein saidmeasurement period of time has a duration of less than or equal to 20seconds.
 9. The method according to claim 1, wherein said measurementperiod of time continues for a predetermined maximum duration or isterminated sooner when the pressure in the measurement capacity reachesa predetermined minimum pressure.
 10. The method according to claim 1,further comprising at the end of said measurement period of time ceasingsaid interrupting of the flow of process gas through said line to saidreference capacity to return the pressure in said reference capacity toa pressure level of the process gas supplied from said source ofpressurized gas.
 11. The method according to claim 1, wherein saidpressure regulator has an inlet coupled in fluid communication with saidsource of pressurized process gas, an outlet, a valve element which isactuable to close said regulator to the flow of process gas and,alternately, to throttle the flow of said process gas through saidregulator, said valve element being actuated by a diaphragm coupled inforce transmitting communication therewith and disposed in fluidcommunication with said process gas to be responsive to a fluid pressureforce thereof, and said regulator further including an adjustable mainpressure setting assembly for applying a select pressure setting forceon said diaphragm, and wherein said method further comprises: adjustingthe main pressure setting assembly of said regulator such that the flowof said process gas therefrom is regulated at an outlet pressure whichis less than a desired outlet pressure for delivering said process gasat said controlled flow rate; applying at about the start of saiddelivery period of time a differential force on said diaphragmindependent of said pressure setting force such that the flow of saidprocess gas therefrom in said delivery period of time is regulated at anoutlet pressure which is about said desired outlet pressure; andterminating the application of said differential force at about the endof said delivery period of time.
 12. The method according to claim 1,including repeating said method to deliver another, discrete batch ofprocess gas for semiconductor manufacturing during a subsequent deliveryperiod of time.
 13. The method according to claim 1, wherein saidcontrolled flow rate is maintained uniform at least during saidmeasurement period of time.
 14. The method according to claim 1, whereinsaid controlled flow rate is maintained uniform throughout said deliveryperiod of time.
 15. The method according to claim 1, wherein said flowcontrol system is adjustable for delivering process gas at a range ofcontrolled flow rates, and said method further comprising using saidactual flow rate to calibrate said flow control system over said rangefor delivering additional batches of said process gas.
 16. The methodaccording to claim 1, further comprising arranging components of saidflow control system along a gas manifold in the form of an elongateddelivery stick having a width less than 1.5 inches.
 17. The methodaccording to claim 1, further comprising measuring the temperature ofsaid process gas being delivered and using the measured temperature toexpress said actual flow rate determined at standard conditions.
 18. Aflow control system for use within a fluid circuit having a source ofpressurized gas to be delivered batchwise at a controlled flow rate to adestination by said flow control system, said flow control system beingoperable in a flow mode for delivering a batch of gas and, alternately,in a no-flow mode, said flow control system comprising: a flow linethrough which gas from said source of pressurized gas can be delivered,a pressure regulator in said flow line to establish a regulated gaspressure in said line, an on/off valve in said line downstream of saidpressure regulator to start and stop said flow mode during which saidgas is delivered for a delivery period of time, a reference capacity insaid flow line upstream of said pressure regulator for use in measuringthe actual flow rate of gas being delivered by said flow control system,a pressure sensor to measure a pressure drop of said gas in saidreference capacity during a measurement period of time commencing afterthe start of a delivery period of time, means in said line upstream ofsaid reference capacity for interrupting the flow of gas from saidsource of pressurized gas to said reference capacity during delivery ofsaid gas by said flow control system, and p1 a controller fordetermining from said measured pressure drop and the rate of pressuredrop in said reference capacity during said measurement period, theactual flow rate of a batch of process gas being delivered and, in casesaid actual flow rate does not agree with a specified flow rate for saiddelivering, adjusting said controlled flow rate in the direction of saidspecified flow rate from said actual flow rate for a subsequent deliveryperiod of time in which another batch of process gas is delivered. 19.The flow control system according to claim 18, further comprising a massflow control valve in said line downstream of said pressure regulator,said controller adjusting a set point value of said mass flow controlvalve for adjusting said controlled flow rate.
 20. The flow controlsystem according to claim 19, wherein said mass flow control valve has arange of possible controlled flow rate settings which extends to 100% ofits full scale with an effective rangeability of 10:1.
 21. The flowcontrol system according to claim 19, wherein said controller includes areference memory storing a mathematical relationship between the actualflow rate and the flow rate setting of said mass flow control valve forreference in determining the size of said adjusting of said controlledflow rate.
 22. The flow control system according to claim 18, furthercomprising a gas manifold in the form of an elongated delivery stickhaving a width less than 1.5 inches, components of said flow controlsystem being arranged along said gas manifold.
 23. The flow controlsystem according to claim 18, further comprising a fixed orifice in saidflow line downstream of said pressure regulator, said pressure regulatorhaving an adjustable pressure setting for adjusting said controlled flowrate.
 24. The flow control system according to claim 23, wherein saidpressure regulator is a dome loaded pressure regulator whose pressuresetting is established by a fluid pressure applied to the dome of thepressure regulator, and wherein said controller at the end of a deliveryperiod of time removing the pressure signal applied to the dome of thepressure regulator to prevent pressure creep at the outlet of thepressure regulator in the no-flow mode of said system.
 25. The flowcontrol system according to claim 18, wherein said pressure regulatorhas an inlet coupled in fluid communication with said source ofpressurized gas, an outlet, a valve element which is actuable to closesaid regulator to the flow of gas and, alternately, to throttle the flowof said gas through said regulator, said valve element being actuated bya diaphragm coupled in force transmitting communication therewith anddisposed in fluid communication with said gas to be responsive to afluid pressure force thereof, and said regulator further including anadjustable main pressure setting assembly for applying a select pressuresetting force on said diaphragm such that the flow of gas from theregulator is regulated at an outlet pressure which is less than adesired outlet pressure for delivering said gas at said controlled flowrate, and a differential pressure setting assembly actuable to apply adifferential force on said diaphragm independent of said pressuresetting force such that together said forces provide a regulated outletpressure of said gas which is about said desired outlet pressure, andwherein said controller operates said differential pressure settingassembly at about the start of said delivery period of time to applysaid differential force during said delivery period of time, andterminates the application of said differential force on said diaphragmat about the end of said delivery period of time.
 26. The flow controlsystem according to claim 18, wherein said means for interrupting is anon/off valve.
 27. An apparatus for semiconductor manufacturing requiringthe delivery of a process gas batchwise at a controlled flow rate duringsaid manufacturing, said apparatus comprising, in combination, a sourceof pressurized process gas, a semiconductor manufacturing apparatus, anda flow control system operable in a flow mode for delivery of a batch ofprocess gas from said source of pressurized process gas to saidsemiconductor manufacturing apparatus and, alternately, in a no-flowmode, said flow control system comprising: a flow line through whichprocess gas from said source of pressurized process gas can bedelivered, a pressure regulator in said flow line to establish aregulated process gas pressure in said line, an on/off valve in saidline downstream of said pressure regulator to start and stop said flowmode during which said gas is delivered for a delivery period of time, areference capacity in said flow line upstream of said pressure regulatorfor use in measuring the actual flow rate of gas being delivered by saidflow control system, a pressure sensor to measure a pressure drop ofsaid gas in said reference capacity during a measurement period of timecommencing after the start of a delivery period of time, means in saidline for interrupting the flow of process gas from said source ofpressurized process gas to said reference capacity during delivery ofsaid process gas by said flow control system, and a controller fordetermining from said measured pressure drop the rate of pressure dropin said reference capacity during said measurement period of time theactual flow rate of a batch of process gas being delivered and, in casesaid actual flow rate does not agree with a specified flow rate for saiddelivering, adjusting said controlled flow rate in the direction of saidspecified flow rate from said actual flow rate for a subsequent deliveryperiod of time in which another batch of process gas is delivered.